1. FIELD OF THE INVENTION
This invention is in the field of processing of combustible solid particles in the presence of a combustion supporting gas, and provides a closed system for generating an inert gas during shutdown, which inert gas is circulated to the various stages of the process to provide a protective atmosphere.
2. DESCRIPTION OF THE PRIOR ART
The problem of accidental ignition of a fuel-oxygen mixture is particularly acute within grinding installations, particularly installations for grinding coal. In such installations, it has previously been proposed to fill the entire installation with inert, oxygen depleted gas when drying and grinding the combustible material. In such installations, exhaust gases may be added to the circulating air as, for example, shown in German Pat. Nos. 720,507 and 748,140.
When such an installation is shut down and cools from operating temperature to the ambient temperature, the gas in the circulatory system which contains a mixture of water vapor, volatile components of the coal, exhaust gases and air, is significantly decreased in volume due to cooling and condensation. The volume loss is replaced by aspiration of fresh air. During this shutdown, therefore, the oxygen content in the installation increases undesirably to such a degree that due, for example, to stirring up carbonization sites, detonations and fires can occur when the installation is again placed in operation.
It has further been proposed, for example, in filling hoppers, to fill the same with inert gases such as nitrogen or carbon dioxide in order to reduce the danger of detonation.
Rendering combustible mixtures within large installations inert by means of introduction of the inert gases such as nitrogen, carbon dioxide, helium, or the like, is not justifiable in many cases for reasons of economy completely apart from the fact that such use of inert gases creates a feeding and transport problem which itself can lead to considerable difficulties.